This application relates to battery packs of the rechargeable type, and in particular to protection of such battery packs during recharging. The application relates in particular to battery packs of the lead-acid cell type.
It is known to provide battery packs, i.e., compact arrangements of one or more battery cells, for various DC power delivery applications. Such battery packs are, for example, commonly used for powering cordless power tools. In recent years battery packs have also been provided for use in jump-starting automotive vehicles. The battery cells of battery packs are typically rechargeable. NiCad battery cells are commonly used for cordless power tool battery packs. More recently lead-acid battery cells have been utilized in battery packs for both cordless power tools and for jump-starting automotive vehicles. Such lead-acid battery cells are sold, for example, by Johnson Controls under the designation "Inspira."
There are various methods of recharging a thin metal film, lead-acid battery pack. The quickest method, and the preferred method for battery packs used for jump-starting automotive vehicles, is to simply leave the battery pack connected to the charging system of the automotive vehicle after the vehicle engine is started and running. This technique can recharge a lead-acid battery pack in a few minutes. However, care must be taken to avoid overcharging lead-acid battery cells, since this can cause overheating and rupture of such cells. Overcharging can result from an over-voltage condition, which could exist if the battery pack is being charged by the charging system of a running automobile engine, the charge regulation system of which has failed. This overcharge danger is normally not presented if slow-rate recharging techniques are used.